Disk drives, also called disk files, are information storage devices that use a rotatable disk with concentric data tracks containing the information, a head or transducer for reading and/or writing data onto the various tracks, and an actuator connected to a carrier for the head for moving the head to the desired track and maintaining it over the track centerline during read or write operations. The actuator is a voice coil motor (VCM) comprising a coil movable through a magnetic field generated by a fixed permanent magnet assembly. There are typically a plurality of disks separated by spacer rings and stacked on a hub that is rotated by a disk drive motor, also called a spindle motor. A housing supports the spindle motor and head actuator, and surrounds the head and disk to provide a substantially sealed environment for the head-disk interface.
In conventional magnetic recording disk drives, the head carrier is an air-bearing slider that rides on a beating of air above the disk surface when the disk is rotating at its operational speed. The slider is maintained next to the disk surface by a suspension that connects the slider to the actuator. The slider is either biased toward the disk surface by a small spring force from the suspension, or is "self-loaded" to the disk surface by means of a "negative-pressure" air-beating surface on the slider.
Contact start/stop (CSS) disk drives operate with the slider in contact with the disk surface during start and stop operations when there is insufficient disk rotational speed to maintain the air bearing. To minimize the effect of "stiction", i.e., the static friction and adhesion forces between the very smooth disk surface and the slider, CSS disk drives often use a dedicated "landing zone" where the slider is parked when the drive is not operating. The landing zone is typically a specially textured nondata region of the disk.
In contrast to CSS disk drives, "load/unload" disk drives address the stiction problem by mechanically unloading the slider from the disk when the power is turned off, and then loading the slider back to the disk when the disk has reached a speed sufficient to generate the air bearing. The loading and unloading is typically done by means of a ramp that contacts the suspension when the actuator is moved away from the data region of the disk. The slider is thus parked off the disk surface with the suspension supported in a recess of the ramp. Load/unload disk drives are commonly used in laptop and notebook computers because the parking of the slider on the ramp away from the disk surface also provides some resistance to external shocks caused by moving or dropping the computer.
In contrast to conventional air-bearing disk drives, contact or near-contact disk drives have been proposed that place the head carrier in constant or occasional contact with the disk or a liquid film on the disk during read and write operations. Examples of these types of disk drives are described in IBM's U.S. Pat. No. 5,202,803 and published European application EP 367510; U.S. Pat. No. 5,097,368, assigned to Conner Peripherals; and U.S. Pat. No. 5,041,932, assigned to Censtor Corporation.
The parking of the head carrier during disk drive power down is typically accomplished by use of file back electromotive force (EMF) generated by the freely rotating spindle motor. When the disk drive supply voltage is removed, the VCM is disconnected from its driver circuitry and connected to a rectifier circuit that is coupled to the spindle motor. The output of the freely rotating spindle motor is converted by the rectifier circuit to a DC current supplied to the coil of the VCM. This causes the actuator to move the head carrier to its parked location. For CSS disk drives, only a relatively small amount of actuator torque is needed to bring the head carrier to the landing zone so that relatively inefficient rectifier circuits are sufficient to apply the necessary current to the VCM. A single-phase, half-wave rectifier circuit using a conventional single silicon diode is commonly used for this purpose. However, for load/unload disk drives, significantly more torque is needed to ensure that the head carrier is fully parked on the ramp, regardless of the actuator position or velocity at power down. The most difficult situation is when the actuator is at rest with the head carrier located near the disk outside diameter immediately adjacent to the ramp. Then there is no time for the actuator to build up momentum so maximum torque is needed immediately. A three-phase, full-wave rectifier circuit with Schottky barrier diodes is commonly used for this purpose. Because there are always two diodes in series with the VCM load, the total voltage drop in this rectifier circuit can be relatively high, thus reducing the DC current available to the VCM. The diodes can be replaced with field-effect transistors (FETs) to reduce the voltage drop, but such devices need to be switched on and off synchronously with each phase of the spindle motor. This requires additional sensing and control circuitry which needs its own DC power source, e.g., a storage capacitor, because the back EMF is insufficient to also power this circuitry.
What is needed for both CSS and load/unload disk drives is a simple, low-cost, power-efficient rectifier circuit for supplying DC current to the VCM to park the head carrier at disk drive power down.